1. Study design: endoscopist-blinded, prospective, randomized controlled trial
2. Subjects
1. Entry criteria: Male or female patients, aged between18 and 75 years undergoing elective outpatient colonoscopy were eligible for the study.
2. Exclusion criteria:
gastrointestinal obstruction or perforation, toxic megacolon, severe uncontrolled inflammatory bowel disease, previous colorectal resection, congestive heart failure, recent acute myocardial infarction or unstable angina, uncontrolled arterial hypertension, renal insufficiency with glomerular filtration rate \< 60 ml/minute/1.73 m2, liver cirrhosis or ascites, pregnancy, lactation, and history of hypersensitivity to any bowel cleansing agents.
3. Sampling design: Consecutive recruitment of consenting patients
4. Variables Predictor
1. group 1 (same day PEG) received 4 L of PEG at 6 hours before procedure on the day of the colonoscopy
2. group 2 (split PEG) received 2 L of PEG at 6:00 p.m the evening before colonoscopy and 2 L of PEG at 4-6 hours before procedure
3. group 3 (SPMC 2) received one sachet of SPMC at 6 p.m the evening before colonoscopy and another sachet of SPMC at 4-6 hours before procedure;
4. group 4 (SPMC 3) received one sachet of SPMC at 6 p.m and the other sachet at 9 p.m the evening before colonoscopy and another sachet at 4-6 hours before procedure.
5. Primary Outcome: Quality of bowel preparation (Ottawa scale)
6. Secondary Outcome: Tolerability, palatability, side effect of the cleansing agents
